Speaking of TPO, has anyone heard of, or had any bad experiences with the material?

I have been specifying a lot of it the last few years, but a rep for a reputable PVC manufacturer showed me a few worn out 6-year-old TPO samples and told me horror stories of how the membranes are manufactured too thin in the U.S. and the seams do not take expansion/contraction well. He claimed that most of the TPO installed in the U.S. within the last half of a decade already needs to be replaced. I realize the rep was trying to sell some PVC membrane, but that was the first time I’d heard of any problems with TPO. It was enough to make me concerned.

Richard, It's probably best to ask some area installers to get you up on a few TPO roofs in your area whose age is known and walk them. That removes the sales element and the second hand evidence.

NRCA technical staff commented last year that the manufacturing quality control on TPO membranes had improved in recent years; the presence of an ASTM standard had also helped, and they were not receiving the same reports of early membrane failures that were more common of membranes installed 8 or more years ago.

On the other hand, there's an interesting issue to keep an eye on - shown to me by a manufacturer. The effective thickness of a TPO membrane is the amount of membrane material on top of the sandwiched reinforcing fabric. Erode that cover material, and the scrim is looking at UV rays - not good. Take a razor, cut some cross sections of the various manufacturers' products, and look at them with your handy dandy Radio Shack 100X hand microscope. The amount of cover over the top of the scrim varies quite a bit. That seems like an important issue to me.

Now - how do you write a spec to qualify that? Or do you just spec the KEE/PVC membranes and not worry about it?

the big issue with TPO is that the manufacturing standard for that product was only adopted in 2003, so before that time, there were a variety of "acceptable " ways to fabricate those membranes. the best protection for that was to use TPO roofs by large, established manufacturers. I've been specifying those roofs for about 8 years because they are slightly less temperature sensitive for installation in the northwest winters.

I am currently a manufacturer's rep. for a KEE based membrane, 5 years ago represented a company that manufactured TPO in the US and have been in the industry 18 years.

There has been a lot of controversy in the roofing industry regarding TPO membranes, everything from the amount of polymer above the scrim, to the effects of the fire retardants on weatherability, to the very different formulas between the different manufactures to many failures in the first formula generations in its US history. It is low priced.

Keep in mind that ASTM needs consensus from its industry members (i.e. manufacturers and others). The ASTM Standard was a necessary move, by the time ASTM came out with the Standard several manufacturers where already producing TPO to their own standards. In order to get consensus the common denominator was lowered. Add to that, that the relatively short history of TPO’s in the US has not been good; you have a Standard that at least with me does not inspire confidence.

The company I currently work for makes a KEE (previously referred to as EIP) and after ten years of asking, ASTM came out with a Standard for KEE in '02. It took ten years for the other roof manufacturers to sign off on it, it did not matter that we had 20 year old roofs with the same base formula at the time without any membrane failures. Since this Standard more closely reflects a product with a proven track record, one could argue that the KEE Standard allows a lot less leeway in what goes into or gets left out of the product.

It is true that the TPO being sold today (recent recipes) are only 8 years old but consider that it took that long to figure out that the first formulas did not cut it. Not all current TPO’s being offered have 8 years of track record.

I assume they will eventually get it right; they may have already gotten it right but only time can judge that.

The experience with the TPO I used to represent was during the first two or three formula changes (1992-2001) and it caused me to lost heart with the product and left.

The following links are articles published by the NRCA; http://www.professionalroofing.net/article.aspx?A_ID=79 http://www.professionalroofing.net/article.aspx?A_ID=79

Here is what Thermoplastic Polyolefin means according to Wikipedia: -A thermoplastic is a material that is plastic or deformable, melts to a liquid when heated and freezes to a brittle, glassy state when cooled sufficiently. -A polyolefin is a polymer produced from a simple olefin, or alkene as a monomer. For example, polyethylene is the polyolefin produced by polymerizing the olefin ethylene. An equivalent term is polyalkene; both terms are mostly archaic, though polyolefin is still used in the petrochemical industry.

The MRCA has a study out, presented at the 2006 RCI Convention, that highlighted the premature failures of such roofing types. Additionally there are numerous studies on the TPO failure to meet the aged fire-resistance criteria as set forth by UL, the seaming failure of the product, and dimensional stability issues for installers. I have access to some of the articles, others are industry foder I think. Bottom line: TPO's are on the bottom of the learning curve in the single-ply market. They will experience the same growing pains as EPDM seam failures, and shattering PVC when they first hit the market. You should ask yourself--is the savings worth being a guinea pig for a new product? As it stands there is not enough track record for maintenance managers, let alone roofers, to know how to repair it. Ask a lot of questions and get a lot in writing and hope that your details are sharp--you should be quite fine then.

Will this mean that the TPO won't be around in ten years, no it doesn't, but it does mean specifier beware.